Robert W. Cattrall

The extraction of cadmium(II) and copper(II) from hydrochloric acid solutions using an Aliquat 336/PVC membrane

Abstract Poly(vinyl chloride) (PVC)-based membranes containing Aliquat 336 as the extractant are used in a study of the extraction of Cd(II) and Cu(II) from HCl solutions. Factors influencing the extraction with these membranes such as the thickness, the composition and the nature of the surface are studied. A mathematical model for the extraction of Cd(II) is used which is based on an extraction mechanism governed by both the chemical kinetics and the membrane diffusion processes. Fitting the model to the extraction data provides values of the diffusion coefficient and the kinetic rate constants of the complexation reaction between the extractant and the extracted species.

Some alkylphosphoric acid esters for use in coated-wire calcium-selective electrodes: Part I. Response characteristics

Abstract The use of several alkylphosphoric acid esters in the production of PVC membranes for use as calcium-sensitive, coated-wire electrodes is reported. The response characteristics, reproducibility, region of linear response for, and effect of plasticizer on, the electrodes are discussed.

The study of a membrane for extracting gold(III) from hydrochloric acid solutions

A membrane is described consisting of Aliquat 336 chloride immobilized in poly(vinyl chloride) (PVC) which extracts gold(III) selectively from hydrochloric acid solutions in the presence of a 500-fold higher concentration of copper(II). Gold is recovered from the membrane by stripping with a thiourea solution. The stability of the membrane is reported in terms of the extent of leaching of the reagent from the membrane in aqueous solutions.

Nafion-based optode for the detection of metal ions in flow analysis

Abstract An optical chemical sensor (optode) is described in which the colorimetric reagent 1-(2′-pyridylazo)-2-naphthol (PAN) is immobilized in a Nafion® membrane. The membrane, which is homogeneous, transparent and mechanically strong, changes color rapidly in the presence of one of several metal ions (Ni(II), Cd(II), Cu(II), Pb(II), Hg(II), Zn(II)), and the color change can readily be reversed by contact with acid. This optode has been incorporated into a modified sequential injection flow system which has been optimized for the determination of Ni(II) in the concentration range 0.02 to 0.12 mM. The advantages of the use of sequential injection with optode membranes are emphasized and the factors which are important in the discrimination between metal ions are discussed.

Spectrophotometric determination of dissolved organic phosphorus in natural waters using in-line photo-oxidation and flow injection

A rapid in-line photochemical digestion for use with flow injection (Fl) to determine the dissolved organic phosphorus (DOP) in natural waters is described. The Fl system includes a simple ultraviolet (UV) photoreactor and uses the tin(II) chloride reduction of phosphomolybdate for the spectrophotometric determination of the dissolved reactive phosphorus (DRP) produced by the photo-oxidation. Samples in the range 0.1–4 and < 0.1 mg l–1 of P can be analysed at rates of 72 and 50 samples h–1, respectively. The effective detection limit of the technique was 0.01 mg l–1. Comparison of the results for DOP obtained using the proposed method were in good agreement with those obtained using standard methods. The DRP could also be determined using the same Fl manifold but without UV irradiation.

Determination of Ammonia in Waste Waters by a Differential pHMethod Using Flow Injection Potentiometry and a Nonactin-BasedSensor

A method is described for the determination of total ammoniacal nitrogen in waters using an ammonium ion-selective sensor based on nonactin. The flow injection method relies on the measurement of the potential of the sensor at two pH values, 6.0 and 9.4, and the use of a mathematical expression to calculate the total ammoniacal nitrogen concentration. The method also compensates for the interference from moderate concentrations of other cations such as potassium and sodium.

Solid phase extraction of zinc(II) using a PVC-based polymer inclusion membrane with di(2-ethylhexyl)phosphoric acid (D2EHPA) as the carrier

A polymer inclusion membrane (PIM) is reported consisting of 45% (m/m) di(2-ethylhexyl)phosphoric acid (D2EHPA) immobilized in poly(vinyl chloride) (PVC) for use as a solid phase absorbent for selectively extracting Zn(II) from aqueous solutions in the presence of Cd(II), Co(II), Cu(II), Ni(II) and Fe(II). Interference from Fe(III) in the sample is eliminated by precipitation with orthophosphate prior to the extraction of Zn(II). Studies using a dual compartment transport cell have shown that the Zn(II) flux (2.58 x 10(-6)mol m(-2)s(-1)) is comparable to that observed for supported liquid membranes. The stoichiometry of the extracted complex is shown to be ZnR(2).HR, where R is the D2EHPA anion.

Theoretical and experimental study of palladium(II) extraction from hydrochloric acid solutions into Aliquat 336/PVC membranes

Abstract The extraction of palladium(II) from its hydrochloric acid solutions into poly(vinyl chloride) (PVC)-based membranes containing Aliquat 336 chloride as both the extractant and the plasticizer was experimentally studied. The results showed that these membranes extracted palladium(II) rapidly and to a very high degree. This property can be used either for the analytical determination of trace levels of palladium(II) or for the recovery of this precious metal from industrial wastewaters and hydrometallurgical solutions. A mathematical model for the palladium(II) extraction into an Aliquat 336/PVC membrane which takes into account the interfacial palladium(II)–Aliquat 336 chloride reaction and the diffusion mass transport through the membrane was developed. The model was fitted to the experimental extraction data to determine the values of the relevant physicochemical constants (i.e. diffusion coefficients and kinetic rate constants).

Mathematical modelling of membrane extraction of gold(III) from hydrochloric acid solutions

Abstract A mathematical model describing the selective extraction of gold(III) from hydrochloric acid solution into a membrane consisting of Aliquat 336 chloride immobilized in poly(vinyl chloride) (PVC) is developed. The extraction rate is assumed to be governed by both the rate of chemical reactions occurring at the interface and the diffusion of the Aliquat 336 chloride species within the membrane. The fairly good agreement between the model and experimental results confirms its validity and shows that the model can be used successfully for the mathematical description and optimisation of membrane extraction utilised in analytical and process systems as well as in environmental chemistry.

Separation of cobalt(II) from nickel(II) by solid-phase extraction into Aliquat 336 chloride immobilized in poly(vinyl chloride)

A solid-phase absorbent obtained by the immobilization of Aliquat 336 chloride in poly(vinyl chloride) is reported to extract preferentially Co(II) from its 7M hydrochloric acid solutions containing Ni(II). Under the experimental conditions there was no extraction of Ni(II) which allowed the complete separation of these two ions. Co(II) was rapidly and quantitatively back-extracted with deionised water. A mechanism for the extraction of Co(II) is proposed based on the formation of the ion-pair A(+)[HCoCl(4)](-) where A(+) is the Aliquat 336 cation. Fe(III) and Cd(II), usually present in Co(II) and Ni(II) samples, were also extracted into the solid-phase absorbent though at a slower rate than Co(II) and they did not interfere with the separation of Co(II) from Ni(II). It was also demonstrated that this approach allowed the complete separation of Ni(II) from the other metal ions mentioned above.